Electromagnetic energy, in the form of radio frequency (RF) energy, is frequently used to produce lesions at a biological site in the human or animal body for many purposes such as, for example, for cardiac ablation purposes, for tumour ablation, etc. RF energy can also be used for heating a site for the treatment of pain management. To apply the RF energy at the required site in the body, an electrode is used as a conductor with an electrode tip forming a first terminal of the circuit and a backplate beneath the patient's body forming a ground electrode for the circuit so that, when the electrode tip is brought into contact with the site, a closed circuit is formed. A problem with this arrangement is that the impedance of the patient's body is high resulting in dissipation of the RF energy through the patient's body rather than being concentrated at the site.
Traditionally lesions have been produced at a site using a single active electrode system. The RF energy is applied to a small electrode tip towards the end of a catheter with an earth connection being made via the patient's body.